// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// File provides direct encoding of bits with arithmetic encoder interface.
#ifndef DRACO_CORE_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_
#define DRACO_CORE_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_

#include <vector>

#include "draco/core/encoder_buffer.h"

namespace draco {

// This coding scheme considers every bit of an (up to) 32bit integer as a
// separate context. This can be a significant advantage when encoding numbers
// where it is more likely that the front bits are zero.
// The behavior is essentially the same as other arithmetic encoding schemes,
// the only difference is that encoding and decoding of bits must be absolutely
// symmetric, bits handed in by EncodeBit32 must be also decoded in this way.
// This is the FoldedBit32Encoder, see also FoldedBit32Decoder.
template <class BitEncoderT>
class FoldedBit32Encoder {
  public:
    FoldedBit32Encoder() {}
    ~FoldedBit32Encoder() {}

    // Must be called before any Encode* function is called.
    void StartEncoding() {
        for (int i = 0; i < 32; i++) {
            folded_number_encoders_[i].StartEncoding();
        }
        bit_encoder_.StartEncoding();
    }

    // Encode one bit. If |bit| is true encode a 1, otherwise encode a 0.
    void EncodeBit(bool bit) {
        bit_encoder_.EncodeBit(bit);
    }

    // Encode |nbits| of |value|, starting from the least significant bit.
    // |nbits| must be > 0 and <= 32.
    void EncodeLeastSignificantBits32(int nbits, uint32_t value) {
        uint32_t selector = 1 << (nbits - 1);
        for (int i = 0; i < nbits; i++) {
            const bool bit = (value & selector);
            folded_number_encoders_[i].EncodeBit(bit);
            selector = selector >> 1;
        }
    }

    // Ends the bit encoding and stores the result into the target_buffer.
    void EndEncoding(EncoderBuffer *target_buffer) {
        for (int i = 0; i < 32; i++) {
            folded_number_encoders_[i].EndEncoding(target_buffer);
        }
        bit_encoder_.EndEncoding(target_buffer);
    }

  private:
    void Clear() {
        for (int i = 0; i < 32; i++) {
            folded_number_encoders_[i].Clear();
        }
        bit_encoder_.Clear();
    }

    std::array<BitEncoderT, 32> folded_number_encoders_;
    BitEncoderT bit_encoder_;
};

}  // namespace draco

#endif  // DRACO_CORE_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_
